Field of the Invention
This invention pertains generally to a method for detecting and locating defective nuclear reactor fuel elements and more particularly to such a method employing a sonic/ultrasonic dual test.
In liquid cooled nuclear reactors radioactive pellets are generally employed as the source of thermal energy. The pellets, enclosed within hermetically sealed thin walled tubular claddings commonly referred to as fuel elements, are expected to withstand extremely high internal temperatures and external pressures. The elements are supported in an ordered spaced array within fuel assemblies having fluid flow channels longitudinally extending along the outer cladding surface of the respective elements. The coolant medium of the reactor is circulated through the assemblies to maintain the elements within a prescribed temperature range. The thickness of the element cladding is a compromise that provides minimum neutron capture cross section and adequate fuel support. However, in the unlikely event of adverse operating conditions, minute rupture of the cladding walls can occur, exposing the interior of the element to small quantities of the cooling liquid. Under such conditions, the probability of resulting contamination to the primary coolant and degradation of the fuel assemblies reliability makes it imperative that a technique be devised to determine the presence of defective elements and their location.
While several methods presently exist for generally indicating the presence of failed nuclear fuel, such as are disclosed in the patents to Weiss et al, U.S. Pat. No. 3,786,257, issued Jan. 15, 1974 and Douet et al, U.S. Pat. No. 3,395,074, issued July 30, 1968, the methods described do not have the capability of identifying the location of specific fuel element failures.
Accordingly, a new method is desired that will identify the presence of defective fuel elements and their specific locations. It is additionally desirable to provide such a method that will have a measure of redundancy. Furthermore, it is advantageous, to provide such a method that will not only identify defective fuel having a cracked cladding wall but also fuel elements having a number of excessively swollen fuel pellets.